The invention relates to the transportation and installation of subsea templates.
The invention provides a method of installing a subsea template which comprises the steps of lifting the template to a position beneath the deck of a semi-submersible drilling vessel, moving the semi-submersible to an offshore site, and then lowering the template from the semi-submersible to the sea bed.
It is preferred that the template is a drilling template, and is lowered to the sea bed from beneath a drilling table of the semi-submersible.
The invention may be applied to the installation of templates for a tension leg platform.
A tension leg platform (TLP) comprises a buoyant body anchored to the sea bed at an offshore site by at least three anchorage (or foundation) templates, there being tension legs extending between the body and the templates, the length of said legs being such that the buoyancy of the body keeps all the legs under tension in all anticipated sea states.
In a particular application the invention provides a method of installing foundations for a TLP (as hereinbefore defined) which comprises the steps of loading at least three anchorage templates onto one or both of the pontoons of a semi-submersible drilling vessel, moving the semi-submersible to the site for the TLP, and then lowering the templates from the semi-submersible to their respective locations on the sea bed.
In one preferred form of the invention a drilling template is moved out to the site using the semi-submersible at the same time as the anchorage templates are moved out to the site.
In this form the drilling template may be lifted beneath the drilling table of the semi-submersible.
In a specific form the drilling template, four foundation templates, subsea pile-driving hammers and a limited number of piles for the drilling template are loaded out in one operation, with the templates loaded onto the semi-submersible in sheltered water.
The invention may include the additional step of piling the template or templates to the seabed using piling means operable from the semi-submersible.
According to a feature of the invention one or more of the templates may be levelled by means of a rotary drill string dependant from a heave compensator mounted on the semi-submersible.
According to another feature of the invention a pin pile slip assembly may be used to handle piles which are installed from the semi-submersible in order to secure one or more of the templates to the sea bed.
The invention also provides a method of levelling a subsea template which includes the step of using a heave compensator dependant from a semi-submersible to adjust the height of the template relative to a fixed pile.
The following procedures are proposed as an advantageous method to loadout, seafasten, transport and install a well drilling template and four six-pile foundation templates from sheltered water to an offshore site.